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UC-NRLF DSS f REESE LIBRARY <)! 'I in: UNIVERSITY OF CALIFORNIA. Accessions No. . Class No. SMOKELESS POWDEK AND ITS INFLUENCE ON GUN CONSTRUCTION. BY JAMES ATKINSON LONGRIDGE, MEM. INST. CIVIL ENG. ; HON. MEM. OF NORTH OF ENGLAND INSTITUTE OP MINING AND MECHANICAL ENGINEERS ; AUTHOR OF <A TREATISE ON THE APPLICATION OF WIRE TO THE CONSTRUCTION OF ORDNANCE*; 'INTERNAL BALLISTICS,' ETC., ETC. E. & F. N. SPON, 125, STBAND, LONDON. NEW YORK: 12, CORTLANDT STREET. 1890. Price 3s. REESE LIBRARY OF THE UNIVERSITY OF CALIFORNIA. ^Heceived , i8g . | ; ^Accessions No..... Class No..... ..... t SMOKELESS POWDER AND ITS INFLUENCE ON GUN CONSTEUCTION. IV BE SMOKELESS POWDER AND ITS INFLUENCE ON GUN CONSTRUCTION BY JAMES ATKINSON LONGRIDGE, MEM. INST. CIVIL ENG. ; HON. MEM. OF NORTH OF ENGLAND INSTITUTE OF MINING AND MECHANICAL ENGINEERS; AUTHOR OF 'A TREATISE ON THE APPLICATION OF WIRE TO THE CONSTRUCTION OF ORDNANCE'; 'INTERNAL BALLISTICS,' ETC., ETC. E. & F. N. SPON, 125, STRAND, LONDON. NEW YORK : 12, CORTLANDT STREET, 1890. V IN the last chapter of my recent treatise on * Internal Ballistics' I alluded to the new powders which were then attracting the attention of artillerists. Keferring to their probable nature, I observed that the introduction of any ingredients which would either increase the volume of gas or its temperature, or both together, would not only explain the apparently anomalous action of these new powders, but probably result in the discovery of a still more powerful agent. Since then this has apparently been accomplished, and the old charcoal powder appears to be doomed to yield to this more powerful rival. But the adoption of this rival, whose properties are as yet only imperfectly known, is not to be viewed without anxiety. Can it be used with advantage, and above all with safety, in our new type forged steel guns ? If not, what changes will its use involve in gun construction ? What will be its effect as regards erosion ? How will it be affected by storage and change of climate ? These are important questions, to which I do not pretend to give complete answers, but I hope that the following remarks will be of some use in directing attention to the problems upon the solution of which future gun construction and ballistic practice largely depend. J. A. LONGKIDGE. GEEVE D'AZETTE, JERSEY. August 1890. CONTENTS I. INTRODUCTORY -. . . . . 1 II. NATURE OF THE POWDER PRODUCTS OF COMBUS- TION POTENTIAL FORCE COMPARISON WITH OLD POWDERS . . . . , 4 III. BALLISTIC EFFECT OF NEW POWDERS IN FRENCH AND GERMAN GUNS COMPARISON OF B.N. AND NOBEL'S POWDER 9 IV. PRESSURES IN THE CHASE WITH NEW POWDER COMPARISON WITH PRESSURES FROM PEBBLE POWDER 17 V. EFFECT OF THE NEW POWDER ON EXISTING GUNS . . 24 VI. INFLUENCE OF THE NEW POWDER ON THE DESIGN OF GUNS 35 VII. CONCLUSION 39 APPENDICES 42 POSTSCRIPT 49 SMOKELESS POWDER. INTRODUCTORY. 1. In few paths of science has the march of progress in the latter part of the nineteenth century been more remark- able than in the development of material for warfare. 2. Less than half a century ago, the heaviest guns in our service were the old 68-pounders, weighing about five tons, and firing, with a charge of 20 Ibs. of powder, a spherical 68 Ib. projectile to which it gave a velocity of about 1500 feet per second a ballistic effect equal to an energy of 1060 foot- tons. 3. The heaviest service gun of the present day is the 110-ton gun, firing a projectile of 1800 Ibs., with a charge of 850 Ibs. of powder, and a velocity of 2100 feet per second, equivalent to an energy of 55,000 foot-tons. 4. In the absence, in this country, of the definite know- ledge of the action and properties of powder (acquired through the researches of M. Sarrau. in France), the adaptation of the powder to the gun, and, vice versa, of the gun to the powder, has been a problem, the solution of which, so far as it has been solved, is of an empirical nature, so that the progress made in gun construction and powder manufacture has been of a somewhat erratic description. 5. After the day of pebble powder came that of P 2 or C and C 2 , then that of prismatic, succeeded by that of brown cocoa, and finally that of the so-called E.X.E., which B 2 SMOKELESS POWDER. a few months ago was looked upon as the ne plus ultra of gunpowder for heavy guns. 6. The line taken by gunmakers has been tolerably con- sistent throughout. They have aimed at reducing the strength of the powder, keeping down the pressure, and making up for this by increased charges, enlarged powder chambers, and increased length of gun. Following out this line they have arrived at charges of one-half, or more, of the weight of the projectile, and at guns of 30 to 40 calibres in length, but with a maximum pressure limited to about 17 tons per square inch. 7. In vain the argument has been urged that, by strengthen- ing the guns instead of weakening the powder, the same ballistic results could be obtained with greater convenience and less expense. It has been shown, both theoretically and practically, that wire guns can be made as safe under a pressure of 30 tons as forged steel guns under a pressure of 17 tons ; but though a few experiments in this direction have been made at Woolwich, they have been made in a half- hearted way, extending over long intervals of time, daring which the construction of the type of* forged steel gun has been rapidly proceeded with, and may be said practically to include the whole of our new armament. 8. These latter guns are designed specially for the use of such powders as the brown cocoa and E.X.E., that is to say, powder of which a very large charge is required. 9. Until quite recently our artillerists have been in a happy frame of mind. They had got, or were very rapidly getting a sufficient supply of large guns of what they thought to be the best possible type, and they had the new E.X.E. powder, the best powder in the world. They had but to rest and be thankful. 10. That rest has been of short duration. From Germany and France came rumours of a new powder giving wonder- ful ballistic results, and at the same time smokeless, or nearly so. 11. Although much secrecy has been maintained with SMOKELESS POWDER. 3 respect to the nature of the new powders, yet the results have been so far made public, that it is no longer doubtful that they will give ballistic results largely exceeding those obtained from cocoa and E.X.E., with considerably reduced charges and no excessive maximum pressure. 12. This being so, the question arises, how far are our new type guns suited to the new powder, and to what extent shall we require a new armament, in order to reap the full advantage of the new powder ? It is proposed to discuss these questions by the light of such knowledge as the author can bring to bear upon the subject. 13. This knowledge is too limited to enable him to produce a "treatise on the use of smokeless powder," but it may perhaps be useful in explaining in some degree the difference of action between the old and new powders, and the approxi- mate results obtained by the use of the latter, both as regards ballistic effect and the development of construction of guns suitable to its use. 14. The subject is divided into the following parts : The nature of the new powder and the results of its de- composition as regards the volume of gas produced per unit of weight, the heat evolved, the temperature of combustion and a comparison with pebble powder, as a type of the old powders, the " Potential " and " Force " of the powder. An examination of the ballistic effects of the new powder in French and German guns. An inquiry into the pressures in the chase of Canet's 15 cm. Q.F. gun, with B.N. powder, and a comparison with a full charge of pebble powder in the same gun. An examination into the effect of using the new ^powder in the existing new type forged steel gun. A few remarks on the influence of the new powder on the design of guns, and finally some general conclusions. B 2 SMOKELESS POWDER. II. NATURE OF THE POWDER PRODUCTS OF COMBUSTION POTENTIAL FORCE COMPARISON WITH OLD POWDERS. 15. The very remarkable results which have been recently obtained from smokeless powder in France and Germany, point to an entire revolution in artillery practice, as well as to a complete revision of the system of gun construction and the formulae of internal ballistics. 16. M. Sarrau's formulae of velocity and pressure, which are very approximately correct for charcoal powders, such as the ordinary black and brown powders, are no longer appli- cable to the case of the new powders which give much higher velocities with smaller charges and reduced pressures. This must consequently lead to modifications in the proportions of guns, if it be admitted that these proportions are de- pendent on the pressures existing in different portions of the gun. 17. The superior results obtained from the new powders are mainly due to the fact that, with them, nearly the whole of the powder is converted into permanent gases, whereas with the old powders only about 43 per cent, is so converted, the remaining 57 per cent, being inert matter existing in the gun in the form of a very finely diffused liquid, which, when cooled down, solidifies ; and is not only mainly the cause of the smoke, but also in all probability one cause of the excessive erosion. 18. Although the chemical constitutions of the new powders are kept as secret as possible, they are probably all closely allied to that of Nobel's smokeless powder, that is to say, the main ingredients are nitre-cellulose and nitro- glycerine, to which is added nitrate or perchloride of ammonia and a little camphor. U IT 171 'ELESS POWDER. SMOK 19. An analysis of the reactions which take place on the explosion of this mixture is given in the Appendix A, and from this it appears that the whole of the products consist of permanent gases and watery vapour, the volume of which amounts to about 705 cubic centimetres for each gramme of powder. 20. Further, that the heat evolved, after allowing for the vaporisation of the water, is about 1 7143 French units per gramme of powder. 21. The mean specific heat of the products is found to be about -1989, and their theoretic temperature about 8673 C. 22. Appendix B contains a similar examination of the results of combustion of pebble powder, which may be taken as a type of the old powders, from which it appears that the following are the results : Volume of gas from 1 gr. of powder .. 286 cm. cube. Gramme units of heat 690*2 Mean specific heat -187 Theoretic temperature of products .. 4:750 C. 23. The temperatures above calculated may be called the " Theoretic or Potential Temperature." The actual tempera- tures are probably not more than one-half, owing partly to the cooling effect of the walls, and partly to the increase of the specific heat at the high temperature and pressure exist- ing in a gun ; but they probably represent the relative effect of the two powders as regards the temperature of the pro- ducts of combustion. 24. The following comparison of the two powders may therefore be made : Pebble. Nobel's. Volume of gas at C. and '76 metres from TinwrlpT 1 gramme ofi 286 690-2 187 4750 705 1714-8 199 8673C. Gramme units of heat evolved from 1 gramme Mean specific heat of products Theoretic temperature of products 6 SMOKELESS POWDER. Potential of NobeTs Powder. 25. By the " Potential " is meant the mechanical equiva- lent of the heat developed by the combustion of unit of weight of the powder, or E Q ; when Q is the quantity of heat evolved, E = 436 in French unities, or 772 in English unities. Now it has been shown that Q = 1*714 units per gramme, or 1714 per kilogramme. 436 x 1714 Therefore, Potential = iQOO = ^^ ' ^ me tre-tons per kilogramme, or 1095 foot-tons per Ib. of powder. 26. In the treatise on ' Internal Ballistics ' * (page 8), there is a table of the " Potentials " of various explosives, and that of pebble powder is given as 460 foot-tons per Ib., or considerably less than the half of that of Nobel's powder ; but, as was there observed, the " Potential " of an explosive must not be confounded with the mechanical effect which may be obtained from it, nor with the pressure developed by its combustion in a closed vessel. 27. At page 50, ' Internal Ballistics/ the symbol "/" was used to denote what is called by M. Sarrau, the " force " of the powder, and it was defined by the relation Po Vp TQ 7 " 273 ' where p Q is the atmospheric pressure = 103 33 kilog. per square decimetre ; V Q is the volume of gases from unit of weight at tem- perature zero and atmospheric pressure ; T is the absolute temperature of combustion. Taking the kilogramme as unit of weight, the volume of gas is, for Nobel's powder, 705 x 1000 cm. 3 or 705 dm. 3 If the actual temperature of combustion be taken as one-half of the theoretic value, or 4326 C., the absolute temperature = 4326 + 273 = 4599. * ' Internal Ballistics,' by J. A. Longridge. Spon, London, 1889. Therefore / = SMOKELESS POWDER. 103-33 x 705 x4599 273 = 1,227,022 kilogrammes per square decimetre. The value of / for pebble powder is given at page 51, ' Internal Ballistics,' as 263,600, consequently the ratio of/, 1227022 as between Nobel's powder and pebble, is = 4 655. Zoobuu 28. The " force," /, as denned by M. Sarrau, is the abso- lute pressure of powder exploded in a close vessel entirely filled ; that is to say of gravimetric density = 1, and with ordinary powder p = f - - , where a is the proportion of non-gaseous matter, which, with ordinary powders, is about 57 of the weight. In Nobel's powder a = 0, consequently p =/A and if A = 1, p =/= 1,227,022 = 122 '7 kilog, per mm. 2 = 78 '52 tons per square inch, which is nearly double that of pebble powder. 29. It is therefore apparent that the Nobel powder is capable of producing much higher pressure than the pebble, and yet in practice it gives higher velocity with less charges and lower pressures. This apparent paradox is easily seen to be due to the absence of inert matter, the whole of the powder being con- verted into gas, instead of only 43 per cent, as in pebble powder, and the total volume of gas being 705 cm. 3 per gramme of powder, against 286 cm. 3 for pebble, whilst at the same time the temperature of combustion is about double. 30. Actual Pressure in gun. The actual pressures in guns are of course much below the calculated values of p, for two reasons : first, because there is a loss of temperature due to the cooling action of the chamber walls, and secondly, because by the time the whole of the charge is burnt, the projectile has moved a considerable way along the chase and so increased the space to be filled by the evolved If, for instance, there be a maximum pressure of 15 tons in 8 SMOKELESS POWDER. the gun (assuming for the moment that there is no loss of heat), we have and making p = 78-52, and p = 15, we get v = v x 3 506 ; so that, if the rate of burning of the powder were suitable, a full charge of gravimetric density = 1 might be fired, and yet the maximum pressure not exceed 15 tons per square inch, which would be attained when the projectile had moved 3 ' 506 times the length of the charge along the chase. 31. Another advantage will probably be the absence of fouling, as the whole of the matter is converted into gases, which leave little or no residuum in the gun. 32. Erosion. As regards erosion, experience must decide. But it may be said that on the one hand, the products of combustion being entirely gaseous, instead of a mixture of gas and fluids, will probable erode less ; whilst on the other hand that the increased temperature and volume will tend to augment that erosion. With the new powder, the temperature no doubt falls more rapidly than with the ordinary powder, because the loss of heat being a function of the difference of temperature between the gases and the gun, is greater with high tempera- tures ; whilst on the other hand, with ordinary powder, it is quite possible that whilst the guns are expanding, heat is communicated to them from the highly heated liquid, arising from the non-gaseous portion of the charge diffused through them. The question of erosion must therefore be determined by experience. So far as our present knowledge goes, the smokeless powder in this respect appears to possess the advantage. SMOKELESS POWDER. III. BALLISTIC EFFECT OF NEW POWDERS IN FRENCH AND GERMAN GUNS COMPARISON OF B.N. AND NOBEL*S POWDER. 33. Formulas for Pressure and Velocity. It is not surprising that the formulae which represent the ballistic action of the old powders are found to be inapplicable to the new powders, and although it is probable that M. Sarrau has already so modified his formula as to make it represent the action of the new powder, it is scarcely likely that the results of his investigations will be made public at present. 34. Although the experimental data published are very limited, it will not be without interest to examine them care- fully. These data are contained in notices of results of firing, obtained at Essen in July and August 1889, with Nobel's powder fired from four different guns, and of the results obtained from the French B.N. powder fired from 10 cm. and 15 cm. guns, or 3*937 and 5*90 inches calibre respectively. 35. An examination of these results leads to a rather remarkable conclusion, which, however, must be taken with all reserve. It is as follows : 1st. The muzzle velocity of the projectile is proportional to the f th power of the weight of charge. 2nd. The maximum pressure in the gun is proportional to the square of the weight of the charge. (1) P = B w 2 . (2) The coefficients A and B are not constants, but are composed 10 SMOKELESS POWDER. of various factors, which are functions of the form, dimension, and rate of burning of the grain in fact, what are called by M. Sarrau the " characteristics of the powder of the weight of the projectile, the calibre of the gun, and the length of travel of the projectile. In M. Sarrau's formula, he introduces another factor A, the gravimetric density, but this is in itself a function of the weight of charge, and of the calibre of the gun. Taking, for instance, M. Sarrau's monomial formula for velocity, as given at page 98, * Internal Ballistics/ where H is a factor containing the " force " and " charac- teristics " of the powder ; w = weight of charge ; A = gravimetric density ; I = length of travel of projectile ; W = weight of projectile ; c calibre of gun. Now, if X = equivalent length of chamber, weight of charge capacity of chamber 7854: c 2 A. substituting which in the above we get <^ and it is the part within the bracket that is represented by A in (1). In like manner Sarrau's formula for pressure is 2 Aw'W* = K o" - 2 > SMOKELESS POWDER. 11 by substituting 7854 for A becomes 1-75 (4) and the part within the bracket represents the B in (2). 36. From this it appears that in passing from the old to the new powders, the index of w is increased from f- to f in the expressions for velocity ; and from 1 75 to 2 in that for pressure, an increase which might be anticipated from the absence of inert matter in the products of combustion of the new powders. The coefficients A and B of course are different with dif- ferent guns, and different brands of powder. 87. The results of the experiments made at Essen in 1889 have been published in the ' Kevue d'Artillerie,' vol. xxxv. These experiments were made with Nobel's powder fired from four different guns, the details of which are given in the following Table, No. I. TABLE I. Number of Gun. I. II. III. IV. 3-287 40 2310 2-20 to 3-54 15-5 to 17-84 Calibre in inches Length of gun in calibres \Veight of gun Ibs 1-968 40 490 ( 0-66 to 0-80 3-81 to 4-10 2-362 40 862 0-66 to 1-21 6-84 to 6-86 2-984 28 904 0-66 to 1-17 I- of charge of projectile .. .. From the results obtained at Essen the following Tables II. and III. have been constructed. Table II. gives the value of the coefficients A and B of formula (1) and (2) ( 35). Table III. gives the velocities and pressures, calculated 12 SMOKELESS POWDER. with these coefficients employed in formulae (1) and (2), and compared with the results actually obtained at Essen. TABLE II. No. of Gun. Number of Rounds Fired. Size of Grain of Powder. Weight of Charge. Weight of Projectile. Coefficients. A. B. in. Ibs. Ibs. T / ^ 1378 66 to '80 3-81 2560 20-0 X* I 5 1181 66 to -792 4-10 2455 20-5 / 2 1969 1 to 1 20 6-86 1527 5-79 I 3 1181 1 to 1-10 6-86 1880 10-20 III. 10 1181 66 to 1-17 15 1429 10-20 6 1969 2-2 to 3-74 15-5 879 0-885 TV 4 1557 3-3 to 3-54 17-84 920 1-215 J. V 2 1181 3-3 17-84 911 1-215 2 1181 3-286 17-84 986 1-760 TABLE III. No. of Gun. Eound . . 1 2 3 4 5 6 7 8 VELOCITY Feet per Second. f Observed 1886 2089 2171 1798 2014 2070 . [Calculated 1887 2104 2165 1797 2018 2077 / Observed 1637 1758 1109 1860 2043 . [Calculated 1640 1761 1109 1890 2019 /Observed 1086 1188 1283 1417 1517 1591 . (Calculated 1047 1174 1284 1429 1535 1607 TV | Observed 1607 1883 2004 2136 2234 2336 2231 2168 JL V . (Calculated 1588 1821 2044 2151 2259 2364 2231 2166 PRESSURES Tons per Square Inch. /Observed 8'46 8-96 13-23 9-72 11-33 13-03 I. (Calculated 8-71 11-83 12-80 8-94 12-16 13-12 ("Observed 6-89 8-60 3-12 jf 10-18 12-48 II. (Calculated 7-00 8-47 3-10 55 10-20 12-34 /Observed 5-76 7-08 8-60 10-50 12-35 13-36 III. (Calculated 4-44 6-65 7-90 10-20 11-77 13-96 /Observed 5-33 8-43 9-02 9-25 11-20 11-69 13-24 14-35 IV. (Calculated 4-28 6-17 8-41 9-63 10-96 12-30 13-23 14-40 French Experiments. 38. The experiments made with the French smokeless powder B.N. were made with two of Canet's quick firing guns of (10 cm.) 3 '937 inch and (15 cm.) 5 '905 inch calibre, each of 48 calibres in length. SMOKELESS POWDER. 13 This is the total length of gun over all, the length of travel of the projectile being about 38 calibres. The powders used were all of the description called B.N. In the 3-937 inch gun, three different lots were used, which may account for the difference of the coefficients A and B, whilst in the 5 905 inch gun the powder was of the same brand throughout. 39. Table IV. gives the values of A -and B, and Table V. the comparison of the observed with the calculated ballistic results, corresponding with Tables II. and III. for the Nobel powder. TABLE IV. Gun Calibre. Number of Rounds Fired. Size of Grain unknown. Weight of Charge. Weight of Projectile. Coefficients. A. B. in. Ibs. Ibs. 3-937 6 Lot 1 5-28 to 8-58 28-6 526 2314 4 Lot 2 7-93 to 8-16 28-6 526 2807 5 Lot 3 7-93 to 9-92 28-6 470 1847 5-905 9 Lot 4 17-64 to 33-08 89-0 198 0172 TABLE V. Gun. Round . . 1 2 3 4 5 6 7 8 9 j j ins. VELOCITY feet per second. 3-937 /Observed 1834 2001 2238 2434 2562 2628 Lot 1 (Calculated 1829 2057 2273 2431 2586 2637 3-937 /Observed 2490 2555 2582 2559 Lot 2 \Calculated 2482 2574 2591 2540 3-937 /Observed 2237 2355 2536 2615 2605 Lot 3 {Calculated 2221 2405 2539 2627 2627 5.Qf)fj /Observed 1666 1962 2303 2428 2603 2674 2671 2750 2746 J7l/cl (Calculated 1716 2008 2325 2470 2611 2680 2680,2750 2750 PRESSURES tons per square inch. 3-937 /Observed 6-54 8-79 11-34 14-20 15-88 16-83 Lotl (Calculated 6-45 8-78 11-47 13-72 16-17 17-04 3-937 /Observed 17-65 17-97 19-62 18-16 Lot 2 (Calculated 17-65 19-47 19-71 18-73 3-937 /Observed 11-75 13-50 16-64 18-10 Lot 3 (Calculated 11-62 14-37 16-60 18-17 /Observed 4-13 6-22 11-77 13-66 16-76 16-83 17-34 18-41 18-54 5-905 (Calculated 4-83 8-36 12-00 14-18 16-38 17-56 17-56 18-81 18-81 14 SMOKELESS POWDER. 40. From these tables it appears that the formulae (1) and (2), above given, represent very closely the results obtained by experiments, and it is therefore probable that the indices 75 and 2 denote the relations between the weight of the charge and the velocity and pressure respectively, at any rate it is so in these guns. 41. A comparison may be made between the French B.N. and the Nobel powder, first as regards the energy of the projectile per Ib. of powder, and second as regards the energy per ton weight of gun. For this purpose take the (10 cm.) 3 '937 inch Canet gun, weighing 4620 Ibs., and compare it with the 3*287 inch Krupp gun, weighing 2310 Ibs. ; the Canet gun being fired with B.N., and the Krupp gun with Nobel's powder of 1557 inch size of grain. It is assumed that the strain on the two guns is the same, that is to say, that the charge shall be such as will give the same maximum pressure in the two guns, and that this pressure shall be 18 '17 tons per square inch, as in the fourth round of this gun in Table V., giving a velocity of 2615 foot- seconds. Therefore, in the Canet gun, which gives Energy per ton of gun 657*1 foot-tons, per Ib. of powder 136*7 foot-tons. 42. In the 3*257 inch Krupp gun, in order to give the pressure of 18* 17 tons, the weight of charge of the * 1557 inch grain Nobel powder is found by the equation P = 1 215 w 2 , whence and the velocity with this charge would be V = 920 w" 75 = 2537 feet per second; SMOKELESS POWDEE. 15 therefore which gives foot-to,,, Energy per ton of gun = 771 7 foot-tons. per Ib. of powder = 205 8 43. If the powder of 0*1969 inch grain were used, the requisite weight of charge would be 4*531 Ibs., and the velocity 2730 feet per second, giving the Energy of the 15 Ib. projectile = 774*7 foot-tons, which gives Energy per ton of gun = 751*2 foot- tons. per Ib. of powder = 171 44. These results are brought together for comparison in the following Table. TABLE VI. 3-937 inch Gun. B.N. Powder. 3-287 inch Gun. 1557 inch Nobel. 3 -287 inch Gun. 1969 inch Nobel. Total energy Energy per ton of gun Energy per Ib. of powder . . 1355 657-1 136-7 795-8 771-7 205-8 774-7 751-2 171-0 45. The results show somewhat in favour of the Nobel powder, both per ton of gun and per pound of powder. 46. It must further be observed that the 3 937 inch gun has the advantage over the 3 287 inch gun, in being a gun of 48 calibres as against 40 calibres in the latter. If the guns had been what is termed " similar guns " and similarly loaded, the velocities would have been the same, but the weight of projectiles as the cubes of the calibres, con- sequently the energy of similar guns increases as the cube of the calibre, which in the present case is in the ratio '3-937\3 ,3-287; 1-719. 16 SMOKELESS POWDER. Consequently, had the guns been similar and similarly loaded, the total energy would have been as 1355 : 788-5; so that not only is the energy of the smaller gun greater than the due proportion, but this is the case under the disadvantage of being the shorter gun. 47. So far then as these experiments go, it appears that the Nobel powder is superior in ballistic power to the B.N. powder. SMOKELESS POWDER. 17 IV. PRESSURES IN THE CHASE WITH NEW POWDER COMPARISON WITH PRESSURES PROM PEBBLE POWDER. 48. In the absence of further experimental' data it is impossible to deduce the relations between the velocity and pressure and the other ballistic elements, such as the length of travel of projectile, weight of projectile, and calibre of the gun, so that the coefficients A and B given above can only be made use of for " similar " guns. 49. It is very important to ascertain as far as may be possible, the distribution of pressures along the chase whilst the projectile is travelling to the muzzle. 50. As has already been shown, there is reason to believe that in a close vessel impermeable to heat, the pressure from the new powder would be about double of that given by the old black powder. Consequently, as in practice the maximum pressure is not greater, it follows that the rate of combustion must be slower, thus giving more time for the projectile to get out of the way, and by thus increasing the space, keep down the pressure. It is also quite possible that the combustion may go on for a considerable time after the maximum pressure is attained, and that thus the pressures towards the muzzle may be greater than with the ordinary powders. 51. As this is a point of great importance relative to the designing of guns, the question requires examination, so far as the limited experience available enables it to be done. 52. Consider the case of the (15 cm.) 5*905 inch Canet c 18 SMOKELESS POWDER. Q.F. 15 cm. gun of 48 calibres with B.N. powder, of which the following are the ballistic elements : CANET'S Q.F. 15 CM. GUN. Calibre of gun ........ 5*905 inches. Length of travel of projectile .. 224*5 Equivalent length of chamber .. 53 Capacity of chamber ...... 1500 cubic inches. of chase ........ 6174 Total capacity of gun ...... 7674 rr/trr j Number cf expansions Z- = 5*116 1500 Weight of charge ........ 33*08 Ibs. Weight of projectile .. .. .. 89 Weight of gun ........ 6*29 tons. Muzzle velocity ........ 2750 f.s. Total energy = 4665 foot-tons. Energy per ton of gun ...... 744' 6 per Ib. powder ...... 141*0 , Maximum pressure ...... 18*81 tons per sq. in. 53. First, it may be asked, what must have been the mean pressure in the gun ? The total energy expended on the projectile was 4665 foot-tons, to which must be added that expended in overcoming friction and expelling the gases, &c. This may be estimated at an additional 20 per cent, making the total energy 5598 foot-tons. Now the area of section of the projectile is 27*4 inches, and the travel 18*4 feet. Therefore, if p be the mean pressure, p = -- -- - = 10*92 tons per square inch. 54. Next, if it be granted that the pressure in a close vessel would be 78 * 53 tons per square inch, and that the pro- ducts of combustion act as a perfect gas, it may be inquired, at what point in the travel of the projectile will the pressure be reduced to the maximum pressure of 18 * 81 tons ? This can only be approximately ascertained in the absence of SMOKELESS POWDEE. 19 knowledge as to the loss of heat due to cooling, but from the considerations set forth in ' Internal Ballistics/ Chapter V., it would appear that this is not very great. Leaving this loss out of account, there is the relation ^ = ( ) , where p W PO and V Q are the original and p and v the final pressures and volumes, and as the volumes are proportional to the lengths, the relation becomes = (= ) . Now let 1 Q be the length of the bore which would be occupied by the charge at gravimetric density = 1, and I the distance from the breech at which the pressure is reduced to p = 18 '81, then 4i9 55. For ordinary powder the space occupied at gravimetric density = 1, is 27 7 cubic inches per Ib. or 1 decimetre cube per kilogramme, and when the charge is thus spaced it is said to be of gravimetric density equal unity. If, however, the space be any other number, say 30 inches to the Ib., the gravimetric density is said to be 56. It is as well to observe, however, that, with the French, " densite gravimetrique " has a different meaning. " Densite gravimetrique "is the weight of 1 cubic deci- metre of powder, not pressed together except by its own weight. Consequently it is evident that the " densite gravimetrique " of a given powder is dependent partly on its absolute density, i. e. specific gravity, and partly on the size of the grain. For instance, the French powder F x has an absolute density of 1 * 750, whilst its gravimetric density is 830 to 870, whilst the WJij-, which has nearly the same absolute density, has a gravimetric density of 1 03 to 1 17. The equivalent of " gravimetric density " in French is not " densite gravimetrique," but '* densite de chargement." c 2 20 SMOKELESS POWDER. 57. As is well known, with the ordinary old powders 27 7 cubic inches is the space occupied by 1 Ib. of powder. But this is not so with the new powder. With respect to this there is much reticence. It is, however, probable that 1 Ib. of this powder may occupy about 31 cubic inches of space, and it is on this assumption that the following remarks are made. Though the conclusions arrived at may not be quite correct, yet they will be relatively so, and will therefore be useful in the examination of the ballistic properties of the new powder. 58. Assuming, then, that the space occupied by 1 Ib. of powder is 31 inches, the length of bore 1 Q occupied by the charge is easily determined. The charge being 33*08 Ibs., and the area of the bore 27 4 inches, we get _ 33-08 x 31 Q _ . Length = = 37-42 inches. 59. Let, then, A D (Fig. 1) represent the bore of the gun* A B the " equivalent length " of the chamber, that is to say, a length of bore whose capacity is the same as that of the chamber, and B D the travel of the projectile, and let A A be the length of the bore which would be occupied by the charge at gravimetric density = 1, that is to say, in the present case 37 42 inches. Then, if the powder were fired in a close vessel, the pressure would be 78 53 tons per square inch ; but as the projectile moves away the space increases, and the contest between the evolution of gas and the increas- ing space goes on until a maximum pressure is reached. If it be assumed that all the powder is burnt at this time, the point Ci, on the curve F C x D, corresponding to this maximum pressure, will denote the position of the projectile, and the ordinates between C and D the respective pressures on the bore as the projectile moves to the muzzle ; the curve F G! D being calculated from the formula l-319 SMOKELESS POWDER. 21 The ordinates between B and C* are indeterminate, and depend upon the rate of evolution of the gas, the weight of projectile and other elements, but it may be assumed that approximately the pressure curve is represented by the curve B G! D! D, and that the point of maximum pressure is at C 1? Tarts SO] 70- 60- 50- 40- JO 20- S F 1 18 -53 torus FIG. 1. and that the total work done on the projectile is represented by the area of the curve multiplied by the area of the bore of the gun. 60. Taking the unit for abscissa in feet, and for the ordinate in tons per square inch, the area of the curves A GI D t D is found to be 210*2, which is the foot-tons per square inch of * The assumption that the curve from B to C t is one-fourth of an ellipse has been found by the author to give very satisfactory results. 22 SMOKELESS POWDER. bore; and multiplying this by 27*4 the area of the bore gives 5761 foot-tons. If from this be deducted 20 per cent, for the resistance, friction, and expulsion of the gases, there remains 4629 foot-tons for the energy of the projectile. This was found by experiment to be 4665 foot-tons. It may therefore be concluded that the pressure curve (Fig. 1) represents, approximately, the pressure in the gun with a 33 Ib. charge of the new powder. 61. Let now this be compared with the corresponding diagram of the same gun fired with a full charge of pebble powder. The capacity of the chamber being 1500 cubic inches, the 1500 full charge will be Appendix C, gives 27-7 Muzzle velocity .. Pressure on projectile = 54 Ibs., which, as is shown in 2570 feet per sec. 22 -00 tons. Therefore the energy is 2570 2 x 89 x 2240 = 4073 foot-tons, which gives Energy per ton of gun per Ib. of powder . . 650 -2 foot-tons. 75-43 62. The following Table shows the comparison between the B.N. and pebble powders in the 5 * 90 inch gun. Powder. Weight of Charge. Weight of Projectile. Muzzle Velocity. Maximum Pressure on Projectile. Total Energy. Energy. Per Ton of Gun. Per Lb. of Powder. Ibs Ibs feet per tons per foot- second. sq. in. tons. B.N. 33-08 89 2750 18-81 4665 744-6 141-0 Pebble.. 54-00 89 2570 22-0 4073 650-2 75*43 SMOKELESS POWDEE. 23 63. If a pressure curve be constructed for the pebble powder in the same manner as above described, and super- imposed upon the curve for the charge of 33 08 Ibs. of B.N. as in Fig. 2, the difference in the distribution of pressure is very strikingly seen. FIG. 2. 64. The maximum pressure on the base of the projectile is 18 * 81 tons per square inch with the B.N., and 22 tons with the pebble powder, but the position at which it attains its maximum is when the shot has travelled 59 inches in the first case, against 16 inches in the second. Again, the final pressure is 5 65 tons per square inch with the B.N., against 3 1 tons with the pebble powder. 24 SMOKELESS POWDER. V. EFFECT OF THE NEW POWDER ON EXISTING GUNS. 65. Enough has now been said to show that the new powder is a revolutionary element in ballistic practice, and that it must consequently exert a corresponding influence on gun construction. 66. It is therefore very important to examine what will be the effect of using such powder in the present new type steel guns, which were designed for the older powders, such as the black and brown prismatic, and the still later E.X.E. powder. 67. These powders are characteristically weak powders, that is to say, they burn slowly and give low pressures in guns. The effect is made up by largely increasing the charges, and in order to give time for the entire combustion and also for utilising the expansive force of the gases, the guns are made very long. In order to contain the large charges and also to reduce the length of the gun, enlarged powder chambers are adopted, with, however, the disadvantage of increasing the size of the breech mechanism, and the strain upon it. 68. Now, in the first place, it may be asked what will be the effect of using the new powders on these guns ? It is claimed for the new powders that, in addition to their quality of smokelessness, they will give vastly higher ballistic results, while they will strain the gun less owing to their low maximum pressure, and this statement has been used as an argument against the necessity of adopting wire guns, instead of the usual forged steel construction. 68a. It is not intended to enter here into the questions of the relative cost of production, the greater freedom from SMOKELESS POWDER. 25 latent defects, the quicker production, or the relative facilities of repairs, in all which respects the wire system has undoubted advantages. But it is desired to show that, if the full advantage is to be obtained from the high ballistic properties of the new powder, it can only be obtained by the use of comparatively high pressure, and consequently, very strong guns, such as can only be produced by the wire system of construction. 69. It is argued that the advantages of the new powders may be utilised in two ways. 70. Either by retaining the present initial velocity with the benefit of a great reduction of pressure, or on the other hand by retaining the present maximum pressure of about 16 tons per square inch, and thus obtaining a very great increase of velocity, although admittedly retaining the disadvantage of a great length of gun. 71. The former alternative is thought to be the better for field guns, as they cannot be lengthened without increase of weight, which is inadmissible. Morever, the weight of cartridges could thus be reduced, consequently more of them could be carried ; whilst it has also been said that, as the pressures are reduced, the strain on the gun carriage would be relieved. 72. This last assertion is, however, a mistake. The effect of the strain on the carriage is proportional to the work done on it, and this varies as the square of the velocity of recoil, which velocity, cseteris paribus, is in proportion to the velocity of the projectile, and has nothing to do with the pressure by which that velocity is created. Consequently, if the muzzle velocity be unchanged the strain on the carriage must be the same, and if, by the use of the new powder, the velocity be increased, the strain on the carriage must be increased correspondingly. 73. This is of course slightly modified by the fact that, in calculating the velocity of recoil, a portion of the weight of the charge must be taken into account, as well as the weight of the projectile, but the effect of this will be comparatively 26 SMOKELESS POWDER. small, and in the case of increased velocity of the projectile, will be far less than the increase due to the increased velocity of the projectile, which is not a function of the maximum pressure, but depends on the mean pressure, which is quite another thing. 74. As regards the length of gun required for the new powder, it is argued that by increasing the pressure it would be necessary also to increase the length of the gun to a practically impossible extent. 75. But this also is erroneous, for it apparently rests on the assumption that the maximum pressure can only be increased by increasing the weight of charge, and that unless the length of the chase be correspondingly increased, part of the charge will be blown out of the muzzle unburnt. 76. Now the maximum pressure depends, not altogether, nor indeed principally, on the weight of the charge, but is chiefly affected by the rate of evolution of the gas, which is regulated almost ad libitum by modifying the form and size of the grain. It is therefore quite practicable to increase the maxi- mum pressure, even if the weight of charge be diminished. 77. This will be the more evident after the following examination of the action of the powder in a gun. 78. In the first place, reverting to Fig. 2 which shows the pressure in the same gun when fired with charges of 33*08 B.N. and 54 Ibs. P respectively; in order to complete the curves the pressures behind the points of the maximum must be indicated. 79. According to M. Sarrau's formulae for ordinary powder, if P be the pressure on the breech, P the maximum pressure on the base of the projectile, making use of Eng- lish unities of pounds for weight and tons per square inch for pressure, w and W being the respective weights of charge and projectile. SMOKELESS POWDEE. 27 Another formula which is said to give better results, especially with slow powders, is _ P " 80. Making use of this latter formula and the weights corresponding to Fig. 2, we find For B.N. powder P = P 1^ = 1 19 P. Oi7 For pebble P = P = 1-30 P. by From which the breech pressures corresponding to the maxima in the diagrams are 22 -38 and 28 -6 tons respec- tively. Setting off these ordinates at the breech the line C^ represents the internal pressure in the gun when the pro- jectile is at Cj, and a line parallel to it, such as g g^ represents the pressure when the projectile is at any other part g. 81. What is most important to note is that whilst the maximum pressure is considerably less with the B.N. powder, although the work done is nearly 15 per cent, more, and the powder charges 40 per cent, less, the pressures are thrown so much further forward, that the B.N. powder if fully utilised will require a very differently proportioned gun, one, namely, in which there is about the same strength behind the point of maximum pressure, but very much greater strength in front of it. 82. Taking for instance the point g lt Fig. 2, at 110 inches from the muzzle, the pressure to be resisted will be 10 tons per square inch with the B.K powder, as against 5 J tons with the pebble. 83. It is quite true that this pressure may be reduced by reducing the charge of the B.N. powder. 84. If, instead of firing with 33 * 08 Ibs., the charge was reduced to 28 f 52 Ibs., the velocity would be the same as that given by the 54 Ibs. of pebble powder, and the maximum 28 SMOKELESS POWDEE. pressure would be reduced to 14 tons per square inch. The length of charge would be 30 inches of the bore. 85. The dotted curve, Fig. 3, is constructed from these data, and being superimposed on the diagram for 54 Ibs. of pebble powder, shows the respective action of the two FIG. 3. 28 54 B.N 54-CC P -53 ; 224-- 5 - powders in the same gun, while producing the same ballistic effects. 86. It is evident that a gun designed to sustain the pressures of the pebble powder is insufficient in strength to sustain the pressures of the new powder in all that part of the chase commencing at about 180 inches from the muzzle. 87. To elucidate this, let an examination be made of the Eoyal Gun Factory 6 a B.L. gun, MAKK IV. of the follow- ing ballistic elements : Calibre Length of rifling .. Capacity of chamber Equivalent length of ditto Total capacity of gun .. Expansions Charge E.X.E Weight of projectile Muzzle velocity Maximum pressure 6 inches. 127 1364 cube inches. 47-03 inches. 5105 cube inches. 3-743. 48 Ibs. 100. 1980 feet per second. 16 % 50 tons per sq. in. SMOKELESS POWDEE. 29 88. In order to compare this gun with the 15 cm. Canet gun, it must first be considered on the supposition that it is lengthened so as to make the travel of the shot the same, viz. 224*5 inches, and then determined what would be the muzzle velocity with the same charge of 48 Ibs. of E.X.E. powder but with a projectile of 89 Ibs. 89. From such data as are at the author's disposal it appears that the " characteristics " of the E.X.E. powder are Log a = -06136 Log/3 = - 1-47844 Making use of which in Sarrau's binomial formulae for velocity gives V = 2444 feet per second. 90. This is the velocity which is taken as a basis of com- parison with the Canet gun fired with B.N. powder. Now, by formula (1) V = 198 to*, and making V = 2441 gives w = 28 -52 Ibs. Then by formula (2) P = -0172w; 2 , which making w = 28 52 gives P = 14 tons per sq. inch for the Canet gun. The comparison is therefore as follows : Charge. Projectile. Muzzle Velocity. Maximum Pressure. Ibs. Ibs. feet per second. tons. Canet 15 cm. gun .. 28 -52 B.N. 89 2444 14 R.G.F. 6 in. Mark IV.) lengthened / 48 E.X.E. 89 2444 16-5 30 SMOKELESS POWDER. Thus, with 2J tons less pressure the Canet gun only requires about T 7 ^ of the charge required of E.X.E. 91. It remains, however, to be seen how the variations of pressure throughout the chase take place in the two guns, and for this purpose recourse must be had to pressure curves, obtained as above described. These, though not accurately correct, represent approximately the real pressures. The curve for the E.X.E. powder is obtained by making use of the formula given in 'Internal Ballistics,' page 172, with FIG. 4. allowance of 20 per cent, for resistance, and is represented by the full line in Fig. 4. 92. The curve for the B.N. powder is obtained as follows : The charge of 28-5 Ibs. at gravimetric density = 1 would occupy 28-5 x 31 = 883 cubic inches, which is equal to 30 inches of- the bore, and the initial pressure in this space would be 78-52 tons per square inch. Therefore the equa- tion to the curve is /30 = 78-52 from which the curve represented by the dotted line, Fig. 4, is constructed. Placing the two curves over each other, as shown in the SMOKELESS POWDEE. 31 figure, it is seen that, although the maximum pressure of the B.N. powder is 3 tons less than that of the E.X.E., yet it is thrown about 39 inches further forward, and that at this point the pressure is about 4 tons per square inch greater than it is with the E.X.E. at the same point in the gun. 93. To pass from this to the Mark IV. gun of the actual length, it is sufficient to cut off from the diagram the excess of length in front of A ; the length up to A being that of the travel of the shot with Mark IV. gun, viz. 127 inches. Then, by subtracting the areas A A! G! C and A A 2 C 2 C from the original areas of the two curves, the remaining areas represent the work done in the two guns if reduced to the length of the actual Mark IV. gun. The original areas are 4537 for each, and the deductions 1299 and 1032; therefore the remaining areas are 3238 and 3505 respectively, representing the energies of the two guns corresponding to muzzle velocities of 2049 and 2132 feet per second. 94. From this it follows that with the E.G.F. 6-inch Mark IV. gun and a projectile of 89 Ibs. nearly the same velocity would be obtained from 28^ Ibs. of B.N. as from 48 Ibs. of E.X.E., and that with 3 tons per square inch less maximum pressure. But this maximum would be about 39 inches nearer the muzzle. 95. Let it now be inquired how the new distribution of pressure would affect the Mark IV. gun ? It may be assumed that this gun has no superfluous strength, especially in front of the trunnions ; indeed, evidence is not wanting to show that the strength of existing guns is deficient rather than excessive in this respect. But let it be assumed that the present strength is suitable for the pressures developed by a full charge of 48 Ibs. E.X.E. powder. 96. Let the strength of the gun be examined at two points, one at 64 inches, the other at 32 inches from the muzzle. At the first point the gun consists of the A tube 1 75 inch thick, and the B l tube 1 '385 inch thick. , 32 SMOKELESS POWDER. At the second point it consists of the A tube, 1 * 35 inch thick, and the BX tube, 1'25 inch thick. 97. According to the principles laid down in the Official Treatise on the Manufacture of Ordnance, 1886, no gun is allowed to be strained beyond three-fourths of the elastic limit of the material, which is fixed at 15 tons per square inch for the A tube, and 18 tons for hoops or the B tube. Consequently the allowed strain is 15 x = 11 '25 tons for the A tube, and 18 x f = 13 '50 tons for the B tube. 98. Making use of the above dimensions, it will be found by the usual formula that the greatest permissible pressure is 9 665 tons per square inch at 64 inches from muzzle, and 6 983 tons per square inch at 32 inches from muzzle. 99. Now, with the E.X.E. powder the pressures at these points are about 10 tons and 8 tons^per square inch respec- tively, so that the gun nearly answers to the required condi- tions; but with the B.N. powder the pressures would be 14 tons and 10 tons per square inch respectively, an excess of 4 tons in the first case and about 3 tons in the second. 100. It is therefore manifest that the strength of this gun in the chase is quite insufficient for a charge of 28 f 52 Ibs. of B.N. powder, and any less charge would give a less ballistic result. 101. It may be objected that the dotted curve Fig. 4 is theoretical, and not based on actual observation, except as regards the maximum pressure, and that the actual results of firing have not shown the guns to be too weak. 102. With regard to the last objection, it has not much weight. A gun may go on firing for a greater or less time without bursting or any visible damage, but not the less surely is it injured every time that it is strained beyond the elastic limit, and this seems to be fully admitted at Woolwich, where, as stated in the Official Treatise, the practice is to limit the maximum strain to three-fourths of the elastic limit. If, therefore, the present guns are not too strong for the present powder, and if the pressure curves be even SMOKELESS POWDER. 33 approximately correct, the guns cannot safely be used with the new powder with increased ballistic effect. 103. The objection against the curve as theoretical carries more weight. Not only is it theoretical, but it depends on the assumption of the pressure in a close vessel being 78 * 52 tons per square inch. The reason for this assumption is given above, and there is nothing in it which appears either improbable or inconsistent with such other facts as are known with respect to this powder. The law of decrease of pressure by which the ordinates and the curves are calculated is a rational law, and in all pro- bability approximately true for the powder gases. 104. Moreover, the velocities deduced from the area of these curves (due allowance being made for other resist- ances) agree very well with the observed velocities, and consequently, whatever be the real form of the pressure curve, its area must be approximately the same as that of the dotted curve, Fig. 4. 105. In the next place, the final ordinate at the muzzle must be the same (if all the charge is consumed), but it is quite possible that the point of maximum pressure may be further to the rear than shown in the curve, Fig. 4. Indeed, the curve may possibly be of such a form as shown in Fig. 5, A B C, the area of which may be the same as that of A B t C. Even in this case the pressures in front of the chase must be greater than with the other powder. It may also be observed that, to permit of the possibility of a curve of the form ABC, the rate of the evolution of gas must be very different from anything previously known. 106. There is another strain besides the bursting strain which must be provided for, viz. the longitudinal strain in the chase of the gun arising from the friction of the products of combustion rushing along the muzzle. 107. The importance of this strain has never been recog- nised by gun-makers, nor do there appear to have been any experiments made to ascertain its magnitude. In ' Internal D 34 SMOKELESS POWDER. Ballistics' reasons have been given for attributing to it a very considerable magnitude, and indeed there can be little doubt on the subject. 108. To what extent the magnitude of this strain will be affected by the use of the new powder can only be conjec- tured. On the one hand, the volume, pressure, and tem- perature of products of combustion are considerably greater. FIG. 5. On the other hand, these products consist of nearly perfect gases, and the coefficient of friction will probably be less than in the mixture of gases and finely diffused liquid arising from the combustion of the old powders. 109. The subject of the longitudinal strain is of such importance that it is inconceivable to the author that gun- makers have taken no steps to ascertain its magnitude and relation to the other ballistic elements. SMOKELESS POWDER. 35 VI. INFLUENCE OF THE NEW POWDER ON THE DESIGN OF GUNS. 110. It has been shown that no great improvement in ballistic effect can be looked for, consistent with safety, with the present guns and the new powder. It is, there- fore, proper to give some attention to the subject of a design of gun suitable for the development of the new explosive. 111. Up to the present, the idea of gun-makers seems to be running in the old groove low pressure and length of gun. The French 15 cm. Q.F. Canet gun is called a gun of 48 calibres, but that is the length over all. The real length is as follows : Chamber 50 inches -f chase 227-5 = 277 -5 inches. It is only slightly chambered, and the equivalent length of the chamber is 53 2 inches. The total capacity of the gun is 7674 cubic inches, and of the chamber 1500 cubic inches, so that it is a gun of 5 '116 expansions, that is to say, a very long gun. 112. But long guns are very inconvenient and objectionable, especially at sea, and the question arises whether it would be practicable to take advantage of the new powder in a short gun, even though it were at the expense of decreasing the efficiency per pound of powder. 113. The gun may be shortened in two ways : First, by an enlarged powder chamber, which, however, has the dis- D 2 36 SMOKELESS POWDER. advantage of increasing the strain upon the breech apparatus ; or, secondly, by increasing the maximum working pressure. 114. To what extent this may be done cannot at present be solved in a general form, inasmuch as the relations be- tween the ballistic effect of the new powder and the ballistic elements, such as calibre of gun, travel and weight of pro- jectile, and " characteristics " of the new powder are unknown in this country. 115. Recourse must therefore be had to the method of curves, and to such limited information as is given in the published results contained in the first part of this paper. The question will therefore be confined to a gun resembling M. Canet's 15 cm. Q.F. gun with a calibre of 5*95 inches, and travel and weight of projectile 224-5 inches and 89 Ibs. 116. Suppose (what might be easily done) a wire gun to be made so as to give the same margin of safety under a pressure of 30 tons as the Canet gun under a pressure of 18-81 tons. By the formula (2), P = 0172 w 2 , and making P = 30, we get w = 41 -76 Ibs., and consequently V = 198 wl = 3253 f.s. Let the capacity of the chamber be 45 5 cubic inches per Ib. of powder, which is the same gravimetric density as in the last round of the Canet gun. (See Table II.) The capacity of the chamber is 1500 cubic inches, and the equivalent length 53 inches, and the length of charge 47 inches. With these data the curve Fig. 6 is constructed, the area of which is 301, which multiplied by the area of the pro- jectile 27-4, gives 8247 foot-tons. Deducting, as before, 20 per cent for resistances, expulsion of gases, &c., there remains 6595 foot-tons, which corresponds to a velocity of 3271 feet per inch, which is very nearly the velocity found by the formula V = 198 wl. 117. The weight of this gun would probably be about 7J- tons, for on the wire construction it could be made con- siderably lighter in proportion than the Canet gun. SMOKELESS POWDER. 37 Therefore the relative efficiency of the two guns would be Energies. Description of Gun. Energy. Per Ton of Per Ib. of Gun. Powder. CanetQ.F 4665 744-6 141 Proposed gun 6598 910-1 158 Showing the decided advantage of the high-pressure gun. 118. It may now be inquired, what would be the length of the proposed high-pressure gun which would have the same ballistic power as the Canet gun ? This may be approximately ascertained from the curve Fig. 6. The difference of energy imparted to the projectile is 1933 foot- tons, to which must be added 20 per cent., making FIG. 6. 30 10- t S3.. c 47'- i KBH 41. 76 Ws > 102' 224.5 2320 foot-tons, which divided by the area 27 * 4, gives 84 68 foot-tons to be deducted from the muzzle end of the curve, and since the mean pressure near the muzzle is about 10 tons per square inch, the length to be deducted is 84-64 10 = 8*46 feet or 103 inches, so that the travel of the projectile would be 122*5 inches and the total length of the gun over all, about 181 inches instead of 283 inches in the Canet gun. 38. SMOKELESS POWDEE. 119. The two guns would have the same ballistic power. The weights would be about the same, and the only difference would be the expenditure of 41f Ibs. of powder instead of 33-081bs. 120. With reference to the higher pressure proposed to be used it is to be observed that the maximum pressure in a gun depends not so much on the charge of powder as on Sarrau's characteristic a, or rather on a 2 , which is in his notation = - , in which/ is the " force " of the powder, a a coefficient T depending on the form of the grain, r the time of total com- bustion of the grain in free air. 121. It is, therefore, obvious that with any given powder for which / has a fixed value, the value of a 2 may be modified by a corresponding modification of a and r, the first of which depends on the form of grain, the second on its density and least dimensions. It is, therefore, simply an object of research to make a powder of which the characteristics a, will give the required pressure. 122. As is easily seen, the higher pressure is given by the lower value of r, whilst at the same time it may be effected by giving such a form to the grain as will give a higher value of a . The practical result of decreasing r is that the evolution of gas is quickened, and the pressure rises at an earlier period of the course of the projectile, because the projec- tile has not had time to move out of the way. 123. It is, therefore, evident that the question of the deter- mination of the " characteristics " of these new powders, and the size and form of grain suited to the different calibres of guns, is one of first-rate importance, and without which future ballistic progress must be a matter of hap-hazard and danger. SMOKELESS POWDER. 39 VII. CONCLUSION. 124. Whilst the superiority of the new powder is incontes- table, there is a danger that must be guarded against. The very fact of its being a more powerful agent renders precaution in its use the more necessary. 125. Its enormous " force " may be practically mitigated in two ways first, by the size and density of the grain, which governs the rate of evolution of gas, and secondly, by a low gravimetric density such as has hitherto been used. By a due adaptation of these, the rate of evolution of the gas has been so proportioned to the space behind the pro- jectile, that the pressures have been kept down to the moderate limit which the new type guns can resist ; but if by any cause, such as a change of constitution of the powder under great variations of climate, or by breaking up of the grains during transport, the rate of evolution of gas is sud- denly increased, then the very high " potential " of the powder may give rise to sudden abnormal increase of pressure, which the guns may be quite unable to resist, and serious accidents may occur. 126. These new powders are certainly more liable to such changes of composition than the old powders, which are simply mechanical mixtures, and therefore it is the more necessary that the guns should be strengthened to the utmost, rather than fined down to meet the requirements of anticipated low pressures. 127. The general conclusions which may be drawn from the preceding remarks are as follows : (1) That the smokeless powder has ballistic properties far superior to the old powders. 40 SMOKELESS POWDER. (2) That the erosive action on the guns will probably be less. (3) That its use in existing guns of the new forged steel type will not lead to any considerable increase of ballistic effect without considerable risk, owing to the increase of pressure developed in the front part of the chase, although the actual maximum pressure on the gun may be less. (4) That to utilise the high ballistic powers of the new powders very strong guns will be required, and that such guns will have to be much stronger in front of the trunnions than those of the new type forged steel guns. That to arrive at very high ballistic results it is not necessary to have guns of inordinate length, but by the adoption of higher initial, instead of low and more uniform pressures, velocities of 3000 feet per second and upwards are attainable with perfect safety. 128. In bringing these remarks to a conclusion, the author may perhaps be allowed to give expression to opinions, which in his own mind amount to convictions, as to the future of gun construction and ballistic effects. 129. The first of these is, that low maximum pressure is a mistake. It has no raison d'etre except the weakness of the gun. It involves a length of gun which for naval use k is most objectionable. No doubt M. Canet has achieved very brilliant results with his 15 cm. Q.F. gun, but this gun is 23 feet 4 inches in length over all. A " similar " gun of 12 inch calibre would be about 46 feet 8 inches long. " Similarly " loaded it would fire a charge of B.N. powder of 264 Ibs., and a projectile of 712 Ibs., with a muzzle velocity of 2750 . feet per second, giving a muzzle energy of 37,330 foot-tons, or 848 3 foot-tons per inch of circumference. Now, as was shown in ( 118), a 15 cm. gun of equal power, firing with a maximum pressure of 30 tons per square inch, would be 15 feet long, and a " similar " gun of 12 inch calibre would be 30 feet long, as against 46 feet 8 inches for the low pressure gun. There can be no doubt which gun is the most suitable for naval service. SMOKELESS POWDER. 41 130. A second conviction is, that guns of a very large calibre are a further mistake, and the author ventures to think that a 9-inch or 10-inch high pressure gun would be sufficient for any effect that is required against the heaviest armour afloat. 131. A third conviction is, that in order to utilise the new powders recourse must be had to the wire system of con- struction, by which alone guns of sufficient strength can be obtained. 132. Lastly, he would express the opinion that no time should be lost in carrying out such a series of experiments as will enable formulae analogous to those of M. Sarrau to be constructed for these new powders, and also for the determination of the tensile strain on the chase caused by the friction of the products of combustion. ( 42 ) APPENDIX A. DECOMPOSITION OF NOBEI/S POWDER AS A TYPE OF THE SMOKELESS POWDERS. According to Nobel's specification, No. 1471/88, 100 grammes of powder contain Grammes. Nitroglycerine 23-10 Nitrocellulose 23-10 Perchloride ammonia 50*35 Camphor 3-45 After explosion these give rise to new products, viz. : From the Nitroglycerine. Grammes. Carbonic acid 13-435 Nitrogen 4-275 Oxygen -814 Water 4-579 Total .. .. 23-10 From the Nitrocellulose. Grammes. Carbonic acid 10-670 Carbonic oxide 6*791 Hydrogen -343 Nitrogen .. 3*112 Water 2-183 Total . 23-10 APPENDIX A. 43 From the Camphor. Grammes. Carbon 2-81 Hydrogen 0-33 Oxygen 0-38 Total .. .. 3-47 From the Perchloride of Ammonia. Grammes. Chlorine 16-63 Oxygen 25-87 Nitrogen 6-47 Hydrogen .. .. 1-39 Total .. .. 50-35 . Certain of the products of the camphor and perchloride unite, and the final result of the decomposition is Grammes. Carbonic acid , 41-26 Nitrogen 13-86 Water 25-24 Chlorine 16-64 Oxygen 2-96 Total . 100-00 VOLUME OF GASEOUS PEODUCTS. The volume of the products in the last paragraph at Centigrade and * 76 metres of mercury would be Cub. Decimetres. Carbonic acid 20-87 Nitrogen 11-04 Watery vapour 31*31 Chlorine .. 8-21 Oxygen 2-08 Total . 70-51 44 APPENDIX A. Therefore, from 1 gramme of powder the volume of gas = *7051 cubic decimetres, or 705*1 cubic centimetres. In the above the water has been considered as in the state of a permanent vapour, though of course that is impossible at Centigrade, but as forming part of the products of com- bustion it is always in the gaseous form, and may therefore properly be comprised among the gaseous products, proper allowance being of course made when the evolution of heat is considered, for the heat absorbed in the vaporisation of the water. HEAT EVOLVED PER GKAMME OF POWDER. Keverting to the 100 grammes of powder, the heat evolved is that evolved in the formation of 42 26 grammes of car- bonic acid and 25 24 grammes of water. The first contains 11-25 grammes of carbon, and the second 2 '80 grammes of hydrogen. Consequently the heat evolved is From Carbon .. 11-25 x 8-08= 90 9 units Centigrade. Hydrogen 2-80x34-46= 96-5 Total .. .. 187-4 but the heat required to vaporise 25 '4 grammes of water is 25-4 x '631 = 15-92 units Centigrade. Deducting which there remains 171-48 units, or for 1 gramme of powder 1*7148 units Centigrade. TEMPERATURE OF PRODUCTS. This can only be given as a comparison with other powders, and not as the real temperature existing in the gun under circumstances when the loss of temperature due to cooling and the specific heat at very high pressure and tem- perature are both unknown. APPENDIX A. 45 The temperature now in question is what might be called the potential temperature or the theoretic temperature, and is calculated on the assumption that there is no loss by cooling, and that the specific heat remains constant. Under these conditions it may be compared with the potential or theoretic temperature of ordinary powders. NOBEL'S POWDER. MEAN SPECIFIC HEAT OP PRODUCTS. Carbonic acid .. .. 41-26 x '172 = 7-097 Nitrogen 13-86 x '173 = 2-398 Watery vapour .. .. 25-40 x '337 = 8-506 Chlorine 16-64 x '086 = 1-431 Oxygen 2-96 x '155 = 0-459 100-00 19-891 Therefore the mean specific heat = 199. TEMPERATURE. Since the heat evolved is 1*7148 units per gramme, or 1714 * 8 units per kilogramme, the temperature will be 1714-8 -- = 8673 C. ( 46 ) APPENDIX B. In order to compare with the Nobel powder, Pebble powder is taken as a type of the old powders, and its composition, as given by Noble and Abel in their * Kesearches on Explosives ' (' Trans. Koyal Society/ 1880), is Parts. Saltpetre -7467 Sulphate (sic) -0009 Sulphur -1007 Carbon -1212 Hydrogen .. -0042 Oxygen '0145 Ash -0023 Water -0095 1-0000 And the products of combustion of 1 gramme at Cent, and * 76 metres of mercury Grammes. Vols. in cm. 3 Carbonic acid -2627 .. 132-9 Carbonic oxide '0468 .. 37-1 Nitrogen.. .. '1099 .. 87-5 Sulphydric acid -0109 .. 9'2 Marsh gas .. '0006 .. 0-8 Hydrogen -0006 .; 6-7 Watery vapour '0006 .. 11-7 4410 285-9 The remaining products consist of about 56 gramme of salts, chiefly of potassium and sulphur, which whilst in the gim are in the form of a liquid diffused throughout the gases and at the same temperature. APPENDIX B. 47 HEAT EVOLVED. The heat evolved from 1 gramme of powder is that due to the combustion of the carbon and hydrogen in it. The carbon is as follows : Grammes. From Carbonic acid .. -2627 X A = '0717 Carbonic oxide .. -0468 X -& = '0201 Marsh gas .. .. -0006 x f = -0005 Total 0-0923 The hydrogen is In Sulphydric acid .. .. -0109 x T V = '00063 Marsh gas -0006 X | = '00009 Water -0006 X i = -00006 -0095 X i = '00106 Total -00184 Consequently the heat evolved is Units. From Carbon to Carbonic acid .. -0717 x 8-08 =0-5793 Carbonic oxide .. -0201x2-473= -0497 Marsh gas .. .. -0005 x 8-08 = -0041 Hydrogen -00184 X34-46 = -0634 6965 From this must be deducted the heat required to vaporise the water, or 0101 x -631 = -0063 Total -6902 MEAN SPECIFIC HEAT. This is given by Noble and Abel as 187. TEMPERATURE (POTENTIAL OR THEORETIC). The heat evolved from 1 kilogramme is 690 '2 units, therefore temperature -7537" == 3690 Cent. APPENDIX C. VELOCITY AND PRESSURE IN 5-905 INCH Q.F. CANET GUN WITH 54 LBS. P. POWDER. Ballistic Elements. c I w W A Log o )8~ Log o a 5-905 224-5 54 89 1 23014 43223 FORMULA FOR VELOCITY. (' Internal Ballistics, p. 137.) V = = m a p - 7 W^ ; tnereiore FORMULA FOR PRESSURE : P = Ka*A(^y \ c 2 / logM 2-84567 logK = -61174 >, * F* = 23014 a 2 = -43223 ,J W* = 64963 A = -00000 A^ = 00000 W^= -97470 c* = 09640 w^ = -86619 -* - 44055 Deduct logV =3-40988 .-. V = 2570 f. s. 2-88486 Deduct logc 2 = 1-54249 logP =1-34237 .-. P = 22-00 POSTSCRIPT. WHILST the above pages were passing through the press I have read an interesting article, in the* United Service Magazine ' of August 1890, by Professor Lewes, of the Eoyal Naval College, on "The Present State of the Powder Question." Agreeing generally in the Professor's con- clusions, I must take exception to one or two of his remarks. I do not agree that a perfect powder is one of which the production of gas goes on until the projectile reaches the muzzle of the gun. Such a powder would be very wasteful, and would carry the region of high pressure much too far forward in the gun. Then, again, I think there must be some mistake in the diagram which is given as representing the pressures in the chase with the three powders P 2 , Bl. Prism, and Br. Cocoa. The areas of the three curves A, B, and C, if correct, must be proportional to the muzzle energies of the projectile. The velocities are proportional to the square roots of the re- spective energies, that is to say, to the square root of the areas of the curves. Now, these three curves are represented by the relative numbers 69 * 5, 76, and 67 5, the square roots of which are 8-33, 8 72, and 8 22, respectively. Consequently, assuming the velocity of 1608 feet per second to be correct for the P 2 powder, the other velocities as represented by the curves would be, Black Prismatic 1683 feet, and Brown Cocoa 1586 feet per second, instead of 1708 and 1798 feet per second as given by Professor Lewes. It is therefore evident that there must be some mistake in the curves shown in the diagram. I am very glad to see that Professor Lewes insists strongly on the importance of the question of the stability of the new powders. H! WIIVl e \<= LONDON t 1'RINTED BY WILLIAM CLOWES AND SONS, LIMITED, STAMFORD STREET ANI> CHAKING CROSS. By the same Author. 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